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Difference between revisions of "EclipseLink/UserGuide/MOXy/Mapping JPA Entities to XML/Lazily Loaded Fields/Properties"

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This example demonstrates how to derive an XML representation from a set of JPA entities using JAXB when a JPA entity has an embedded ID class.
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This example demonstrates how to derive an XML representation from a set of JPA entities using JAXB, when a JPA entity has an embedded ID class.
  
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== JPA Entities ==
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= JPA Entities ==
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The following JPA entities are used in this example:
  
 
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== JAXB Bindings ==
 
== JAXB Bindings ==
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Here, the XML accessor type type is set to '''FIELD''' for all model classes. This can be set as a package level JAXB annotation.
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For this example the XML acessor type will be set to FIELD for all the model classes. This can be set as a package level JAXB annotation.
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=== Target Object ===
 
=== Target Object ===
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This entity uses the '''@XmLCustomizer''' EclipseLink extension to extend the JAXB specification. Because the relationship is bidirectional, we'll also use the '''@XmlInverseReference''' EclipseLink extension.
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As we require support beyond the JAXB spec, we will make use the EclipseLink extension @XmlCustomizer. Also since the relationship is bidirectional, we will use the EclipseLink extension @XmlInverseReference.
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</source>
  
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If we want the content of the EmployeeId class to be embedded in the complex type corresponding to the Employee class then we can change the XPath on the mapping for the "id" property to be self or ".".
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To have the '''EmployeeId''' class be embedded in the complex type corresponding to the '''Employee''' class, change the XPath on the mapping for the '''id''' property to be self or '''.'''.
  
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Then we must specify the XPath to the XML nodes which represent the ID.
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Then specify the XPath to the XML nodes which represent the ID.
  
 
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=== Source Object ===
 
=== Source Object ===
  
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If the target object had a single ID then we would use @XmlIDREF. Since the target object has a compound key, we will mark the field @XmlTransient, and use the EclipseLink extension @XmlCustomizer to set up the mapping.
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If the target object had a single ID then we would use '''@XmlIDREF'''. However, since the target object has a compound key, we will mark the field '''@XmlTransient''', and use the EclipseLink extension '''@XmlCustomizer''' to set up the mapping.
  
 
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</source>
 
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An XMLObjectReferenceMapping will be created.  The mapping will include multiple key mappings.
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An '''XMLObjectReferenceMapping''' will be created.  The mapping will include multiple key mappings.
  
 
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Revision as of 10:00, 23 May 2011

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This example demonstrates how to derive an XML representation from a set of JPA entities using JAXB, when a JPA entity has an embedded ID class.

JPA Entities =

The following JPA entities are used in this example: 

@Entity
public class PhoneNumber {
 
    @ManyToOne
    @JoinColumns({
        @JoinColumn(name="E_ID", referencedColumnName = "E_ID"),
        @JoinColumn(name="E_COUNTRY", referencedColumnName = "COUNTRY")
    })
    private Employee contact;
 
}
@Entity
@IdClass(EmployeeId.class)
public class Employee {
 
    @EmbeddedId
    private EmployeeId id;
 
    @OneToMany(mappedBy="contact")
    private List<PhoneNumber> contactNumber;
 
}
@Embeddable
public class EmployeeId {
 
    @Column(name="E_ID")
    private BigDecimal eId;
 
    private String country;
 
}

JAXB Bindings

Here, the XML accessor type type is set to FIELD for all model classes. This can be set as a package level JAXB annotation. 

@XmlAccessorType(XmlAccessType.FIELD)
package com.example.model;
 
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;

Target Object

This entity uses the @XmLCustomizer EclipseLink extension to extend the JAXB specification. Because the relationship is bidirectional, we'll also use the @XmlInverseReference EclipseLink extension. 

@Entity
@IdClass(EmployeeId.class)
@XmlCustomizer(EmployeeCustomizer.class)
public class Employee {
 
    @EmbeddedId
    private EmployeeId id;
 
    @OneToMany(mappedBy="contact")
    @XmlInverseReference(mappedBy="contact")
    private List<PhoneNumber> contactNumber;
 
}

To have the EmployeeId class be embedded in the complex type corresponding to the Employee class, change the XPath on the mapping for the id property to be self or ..

Then specify the XPath to the XML nodes which represent the ID. 

import org.eclipse.persistence.config.DescriptorCustomizer;
import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.oxm.mappings.XMLCompositeObjectMapping;
 
public class EmployeeCustomizer implements DescriptorCustomizer {
 
    public void customize(ClassDescriptor descriptor) throws Exception {
        XMLCompositeObjectMapping idMapping = 
            (XMLCompositeObjectMapping) descriptor.getMappingForAttributeName("id");
        idMapping.setXPath(".");
 
        descriptor.addPrimaryKeyFieldName("eId/text()");
        descriptor.addPrimaryKeyFieldName("country/text()");
    }
 
}

Source Object

If the target object had a single ID then we would use @XmlIDREF. However, since the target object has a compound key, we will mark the field @XmlTransient, and use the EclipseLink extension @XmlCustomizer to set up the mapping. 

@Entity
@XmlCustomizer(PhoneNumberCustomizer.class)
public class PhoneNumber {
 
    @ManyToOne
    @JoinColumns({
        @JoinColumn(name="E_ID", referencedColumnName = "E_ID"),
        @JoinColumn(name="E_COUNTRY", referencedColumnName = "COUNTRY")
    })
    @XmlTransient
    private Employee contact;
 
}

An XMLObjectReferenceMapping will be created. The mapping will include multiple key mappings. 

import org.eclipse.persistence.config.DescriptorCustomizer;
import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.oxm.mappings.XMLObjectReferenceMapping;
 
public class PhoneNumberCustomizer implements DescriptorCustomizer {
 
    public void customize(ClassDescriptor descriptor) throws Exception {
        XMLObjectReferenceMapping contactMapping = new XMLObjectReferenceMapping();
        contactMapping.setAttributeName("contact");
        contactMapping.setReferenceClass(Employee.class);
        contactMapping.addSourceToTargetKeyFieldAssociation("contact/@eID", "eId/text()");
        contactMapping.addSourceToTargetKeyFieldAssociation("contact/@country", "country/text()");
        descriptor.addMapping(contactMapping);
    }
 
}


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